Magnesium diboride superconductor doped with different boride compounds by high energy ball milling.

摘要

The study of 5 at.% MeB2 doped MgB2 (Me = Ta, Ti, Nb and Cr) was carried out using the High Energy Ball Milling (HEBM) technique and Hot Isostatic Press (HIP) process. Each compound was milled separately for 120 min and then they were mixed and milled at 60 min, 120 min, 180 min, 300 min and 600 min. The milled materials were HIPed at 1000°C and 30,000 psi for 24 hours. Both powder and HIPed materials were characterized in the structural properties with X-ray diffraction (XRD); crystallite size, strain, composition and lattice parameter were determined with this technique. The superconducting properties were carried out on the HIPed material with the use of the physical property measurement system (PPMS); critical temperature (Tc), critical magnetic field (Hc2), connectivity and electron scattering were found.;In the structural properties of the powder materials, as the milling time increased, reduction in crystallite sizes and increase in strain was observed. Additionally, decomposition of MgB2 in Mg and B elements occurred. Moreover, with the HIP process the increase in crystallite sizes, the decrease in strain and the reorganization of the structure was determined.;In the superconducting properties, the MgB2 -- 5 at.% TaB2 material had the highest Hc2 (25 K) value at 180 min of milling time with 7.539 T, while the Tc for the same sample was 38.48 K. These results showed that with TaB2 at 5 at.% material, it is possible to increase Hc2 without decreasing Tc in MgB2.;However, the MgB2 -- 5 at.% CrB2 material showed a decreased in Hc2 and Tc for all milling times, which suggests that CrB2 is not a good dopant material for MgB 2.;The residual resistivity ratio (RRR) is an indicator of the electron scattering; RRR decreased with the increase in electron scattering approaching to 1 for very high defect concentration. In this research the RRR parameter decreased with the increasing in milling time, while the Hc2 property increased with the increase in RRR.